>> RF 433Mhz RADIO COMMUNICATION WITH AN ARDUINO

In this technological day and age - who needs wires for communication!

While shopping around recently for some hardware I came across from 433Mhz RF radio components that I just had to pick up and see what I could do with them. The components I purchased were the 433Mhz ASK modulation based RF Link Transmitter and RF Link Receiver. So how difficult is it for two Arduino's to communicate over the 433Mhz frequency band?

But what is the 433Mhz frequency band?

Officially, it is called LPD433 which stands for Low Power Device 433Mhz - which is a UHF radio band that is license free where devices are allowed to operate. It is commonly available and you may even be using it without knowing - if you have a garage door; or some remote control for lighting; chances are it will utilize the 433Mhz frequency band.

The hardware is also extremely cheap - so getting started isn't going to cost a lot.

The first step for doing anything with these components was to get access to the data sheets for each one to know exactly which PINs on them mean what and where they should be connected. The two components I purchased had data sheets hosted on sparkfun:

• RF Transmitter Module
• RF Receiver Module

The Arduino world is full of open-source libraries that one can find easily and thankfully; someone has already implemented the ASK modulation logic for processing the raw signals from these components. I first came across the VirtualWire library - but, it has been since merged into the more advanced RadioHead library covering a large range of hardware.

The library is extremely well documented - a good sign for the community!

The subsection of the library we want to use is called RH_ASK that is designed specifically for these components. Of course; they have some great simple examples which can be used out of the box - in fact, they are the basis for the demo which I have prepared.

The library defaults at 2000 baud and matches RX to PIN11, TX to PIN12 and PPT to PIN10.

In addition to aligning the components to use this configuration (to avoid changes) and I also added on the receiving device an LED that we plan to turn on and off based on values sent from the transmitter. The fritzing diagram for the receiver is as follows:

On the transmitting device, I have wired up a push button with a 220Ω resistor to detect presses on the Arduino (fritzing diagram below) to allow for some interaction. The idea is that when the button is pressed; the LED should light up on the receiver and turn off when it is rreleased.

Notice that there is a small antennae (approx 13cm) that must be connected to both components.

• ask_transmitter.ino
• ask_receiver.ino

The complete sketches are available above - the library isn't limited to sending a single value; up to sixty-seven bytes of data can be sent in each packet. Detailed information on how it is implemented is available on the RadioHead libraries website - a good read for sure.

The console log of the transmitter should look like:

• ask_transmitter
  ---------------
  
  author:  Aaron Ardiri
  version: Nov 25 2015
  
  :: ASK init ok
  :: ASK send()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK send()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK send()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK send()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK send()
     ASCII: station00:1'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x31
  :: ASK send()
     ASCII: station00:1'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x31
  :: ASK send()
     ASCII: station00:1'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x31
  :: ASK send()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK send()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30

... and the corresponding console log of the receiver:

• ask_receiver
  ------------
  
  author:  Aaron Ardiri
  version: Nov 25 2015
  
  :: ASK init ok
  :: ASK recv()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK recv()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK recv()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK recv()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK recv()
     ASCII: station00:1'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x31
  :: ASK recv()
     ASCII: station00:1'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x31
  :: ASK recv()
     ASCII: station00:1'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x31
  :: ASK recv()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30
  :: ASK recv()
     ASCII: station00:0'
     HEX:   0x73 0x74 0x61 0x74 0x69 0x6F 0x6E 0x30 0x30 0x3A 0x30

Originally the sketch had a 500 millisecond delay (as in video) which could have some latency in transmission. I have since updated it to 25 millisecond delay and the reponse is almost instananeous - keep in mind the smaller the delay; the more broadcasting on 433Mhz frequency.

I may do some further investigation to see if I can get multiple transmitters talking to the receiver at the same time as it could open up a very cheap and simple way to have a number of sensors communicate to each other over fairly long distances. In the mean time; do not go out there hacking people's garage door openers or other devices.